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Full text of "Alaskan glacier studies of the National Geographic Society in the Yakutat Bay, Prince William Sound and lower Copper River regions"

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386                                  ALASKAN GLACIER STUDIES
(b) a main ice tongue whose stream flows into Eyak Lake, which drains by Mountain Slough over the Copper River delta to the Pacific Ocean; and (c) two smaller distributaries, which send streams directly to the head of Orca Inlet.
Since we have not visited Shephard Glacier we lack further information about it. There are two unnamed ice tongues to the north, each of which is over half a mile in width. Their streams join the one from Shephard Glacier which flows to the head of Orca Inlet.
Glaciers of Sheep and Simpson Bays. The mountains at the head of Sheep and Simpson Bays rise precipitously to a considerable height and have small glaciers, none of which have been mapped or observed from nearer than the entrance to these bays. The fiord walls are very steep, the northwestern side of Sheep Bay rising to an elevation of 2520 feet within a mile of sea level. There are many large cirques in these mountains, due to extensive former local glaciation. Within Sheep Bay the depth of water varies from 144 to 300 feet with a shallower inner portion studded with islands, suggesting that there has never been a very great glacier extending from the head of this inlet. The upper part of Simpson Bay is also irregular, with large peninsulas.
Glacial Erosion in Orca Bay and Orca, Inlet. These arms of the sea are typical fiords and have the usual characteristics of marked modification by glacial erosion. The higher mountains at the head of Orca Inlet and Simpson and Sheep Bays, have large areas of rounded, bare rock and many cirques and hanging valleys. Some of the lower slopes of the fiord walls are much oversteepened by glacial erosion, the southeastern side of Orca Inlet, between Orca cannery and Cordova, for instance, rising to 1600 feet within a half mile of sea level, but only 898 feet in the next half mile. All of the fiord walls do not rise so steeply, however, and parts of outer Orca Bay have rather low, sloping shores. In Orca Inlet the smoothing by Lie former Ice tongue extends up to 2300 feet, and north of Orca Bay to 2500 feet, as estimated by Grant and Higgins.1 In the town of Cordova observations of the direction, of striae, by the junior author in 1910, make it clear that the ice of one of the expanded lobes of Shephard Glacier advanced down the valley of Eyak Lake, and spilled over into Orca Inlet. This resulted in notable shortening of the spur upon which Cordova is built.
Glacial erosion below sea level is shown very well by the detailed soundings on the Coast Survey charts.2 Orca Bay has a depth of 198 feet at Salmo Point, and deepens rapidly to 744 feet opposite Simpson Bay, 7^ miles from Salmo Point; but this is an exceptional depth, for in the next 11 miles, westward to the mouth, the depth is only 400 to 500 feet. The portion opposite the mouth of Simpson Bay may be a basin due to glacial scooping. Near its outer edge there are rock reefs including Hanks Island, Gatherer Rock, and a series of shoals which extend nearly halfway across Orca Bay. Sheep Bay, which is as wide at the mouth as Orca Bay at this point, does not appear to have a hanging relationship to Orca Bay. Simpson Bay occupies a submerged hanging valley, being 120 to 336 feet deep at the entrance, while just outside the lip of the hanging valley, the depth is 516 feet, a discordance of at least 180 feet. Windy Bay, on the southern side of Orca Bay, is a submerged hanging valley, having a depth of 114 to 174 feet at the entrance and hanging,546 feet above the bed of Orca Bay, which is here 720 feet deep. Both Canoe Passage and Hawkins Island Cutoff are apparently hanging valleys, but there is an unknown thickness of deposit in each.
i Grant, U. S. and Higgins, D. F., Bull. 449, U. S. Geol. Survey 1910, p. 18. * U. S. Coast and Geod. Survey, Charts 8520 and 8550.